Renovate Cognitive Networks under Spectrum Unavailability

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Renovate Cognitive Networks under Spectrum Unavailability

Anwer Al-Dulaimi, Saba Al-Rubaye, and Hamed Al-Raweshidy School of Engineering & Design, Brunel University, London, UK {anwer.al-duliami, saba.al-rubaye, hamed.al-raweshidy}@brunel.ac.uk

Abstract—Spectrum availability is a decisive factor for the continuity of Cognitive Network (CN) broadcast. Cognitive networks lease the spectrum temporarily whenever the primary users went off. Thus, localized wireless changes within CN cells rapidly affect the transmissions of the cognitive radios. This situation becomes more complicated for cognitive mesh networks when establishing a link over many cells. Therefore, link formation failure may cause complete disruption at certain sites of the network. A mathematical model is first introduced to study the delay impacts of the spectrum unavailability on the CN’s which has been analyzed as the most severe cause for the CN failures. In this paper, a new subnet called Cognitive Radio over Fibre (CRoF) is proposed as an alternative for the wireless links between cognitive base stations every time there is no free spectrum to communicate. In this proposed solution, the CRoF subnet splits the CN into zones according to the number of expected users and free spectrum available. Then, CRoF base stations are placed at the edges of the structured zones to act as seniors for other cognitive cells. Consequently, a new management for secondary networks is achieved for local spectrum access. Initial Opnet simulations show 11% time savings during packet delivery for the CRoF designed scenarios in comparison with traditional CN’s. The proposed CRoF subnet provides a permanent solution to restore service delivery for the CN’s affected by wireless changes.

Keywords-Cognitive Radio Network; Mesh; Zones; Spectrum Unavialability.

I. INTRODUCTION Privatization of the telecommunications industry coupled with technological advancements and economic liberalization has stimulated competition among Wireless Service Providers (WSPs) and driven down the prices. In addition, the transformation from second generation (2G) mobile telephony to third generation (3G) technologies has also boosted this competition to a great extent resulting in numerous WSPs in one geographic region [1]. The conventional approach to spectrum management is very inflexible in the sense that each operator is granted an exclusive license to operate in a certain frequency band. However, with most of the useful radio spectrum already allocated, it is becoming exceedingly hard to find vacant bands to either deploy new services or enhance existing ones [2]. Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum

opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications [3]. Wireless mesh networks (WMNs) are known for their self configuration ability to form a network on power-up, for their easy installation and maintenance, and for their cost effectiveness. Mesh nodes, or simply nodes, can hear each other’s broadcasts, and distributively make a self-formed multi-hop network. Nodes may act as sources/clients when they themselves generate data traffic or as relays/routers when they forward traffic for other nodes through multi-hop routing. When a route breaks due to a node’s (or a link’s) failure, nodes can auto-recover by rediscovering an alternate routing path without the intervention of a central unit or an administrator. WMNs are also cost effective as they eliminate the need for a core network; i.e., nodes no longer require a wireless router to connect to each other since each node acts as the client and as a router [4]. A key factor for the mesh-cognitive radio networks is the establishment of link paths between many cells. This requires the availability of the spectrum at all cells sites that a certain link is passing through. The spectrum unavailability could leads to interrupt the secondary network services. This spectrum unavailability can be caused by:

1. The absence of some operational cognitive nodes along a trajectory between two distant points. The spectrum at the cells where the link overtakes could be used entirely by the primary users. This will block the cognitive nodes for unknown periods of time until spectrum ‘white spaces’ are revealed again. One additional assumption for such interruption, that the free spectrum at these cells may not satisfy the Quality of Service (QoS) requirements. Hence, a major service disruption occurs either at one cell or even on multiple cells locations. 2. Cognitive nodes may go selfish and ignore the requests to form transmission routes with other neighbouring nodes. This uncooperative behavior triggers a significant degradation in the performance of the cognitive network especially if this action was committed by many nodes. A terrestrial collapse for the services at these nodes locations is expected.